Benthic Plume Generation and Sedimentation from a Commercial-Scale Model of Polymetallic Nodule Mining in the Clarion–Clipperton Zone

The deep-sea mining industry faces opposition from those concerned about potential environmental impacts, such as the effect of sediment plumes created by mining activity. To assess the magnitude of those effects, the spatial extent of the plume, the total suspended sediment load, and the extent and thickness of the resulting sedimentation should be quantified. Here, we present a commercial-scale model of benthic plume generation from polymetallic nodule mining in the Clarion–Clipperton Zone (CCZ). This quantifies the spatial extent of the plume and resulting sedimentation after 435 days of collecting polymetallic nodules on the seafloor in the NORI-D contract area in the eastern CCZ. The model is based on a previously published hindcast model from a smaller test mining operation, scaled up to reflect commercial operations. It consists of mining a 12,624 km mining path with one collector vehicle, reflecting a realistic first phase of mining in the area. The model shows that most of the suspended sediment remains very close to the mined area, staying largely below ~8 m above the seafloor. The plume would grow to only 0.029% of the NORI-D water volume at its largest and disperses quickly over 2–5 days when operations cease. The majority of the sediment from the plume would be deposited on the mined area, with 86.7% of sediment falling within 10 m of the nearest mining path. Sedimentation thickness is dependent on the local topography and is generally 50 to 100 mm, and up to 267 mm in limited low-lying areas. Outside of the mined area, thicknesses rapidly reduce with distance from the mining path, and all thicknesses greater than 5 mm occur within 1 km of the nearest collector track. Outside of the mined area, sedimentation is characterised by very gradual sedimentation at rates on the order of microns per day or less. The results suggest that the effects of the plume and sedimentation from mining are largely limited to the mined area.